1. Field of the Invention
The present invention relates to an encapsulant capable of collective encapsulation on a wafer level, particularly to an encapsulant substrate, a semiconductor-device-mounting substrate and a semiconductor-device-forming wafer that are both encapsulated with the encapsulant substrate, an individual semiconductor apparatus cut from the semiconductor-device-mounting substrate or the semiconductor-device-forming wafer, and a method for producing a semiconductor apparatus using the encapsulant substrate.
2. Description of the Related Art
Various methods have been proposed and studied for encapsulating, on a wafer level, a semiconductor-device-mounting surface (also simply referred to as a device-mounting surface, hereinafter) of a substrate on which semiconductor devices are mounted, or a semiconductor-device-forming surface (also simply referred to as a device-forming surface, hereinafter) of a wafer on which semiconductor devices are formed. Example of these methods include encapsulation by spin coating, encapsulation by screen printing (Patent Document 1), and use of a composite sheet obtained by coating a film support with a hot-melt epoxy resin (Patent Documents 2 and 3).
Among these methods, the following method has been put in practical use to encapsulate the device-mounting surface of a substrate on which semiconductor devices are mounted (also referred to as a semiconductor-device-mounting substrate, or simply a device-mounting substrate, hereinafter): A film with an adhesive layer provided each on its both sides is attached to, or an adhesive is applied by spin coating to an upper part of a metal substrate, a silicon-wafer substrate, or a glass substrate; semiconductor devices are then mounted on the device-mounting surface of the substrate by arranging and bonding the devices; and the device-mounting surface is then encapsulated with a liquid epoxy resin or an epoxy molding compound by compression molding under a heated condition (Patent Document 4). Similarly, a method, involving encapsulating the device-forming surface with a liquid epoxy resin or an epoxy molding compound by compression molding under a heated condition, has been put in practical use to encapsulate the device-forming surface of a wafer on which semiconductor devices are formed (also referred to as a semiconductor-device-forming wafer, or simply a device-forming wafer, hereinafter).
Such methods enable encapsulation of a wafer or a substrate, such as a metal substrate, having a small diameter, e.g., about 200 mm (8 inches) without a serious problem, whereas encapsulation of the device-mounting surface or device-forming surface of a wafer or a substrate having a large diameter, e.g., 300 mm (12 inches) or more according to these methods brings a serious problem in that the substrate or the wafer is warped, or the wafer is damaged, owing to contraction stress of a resin, such as an epoxy resin, during curing for the encapsulation. Such contraction stress may disadvantageously cause some of the devices to peel away from the substrate during encapsulating the device-mounting surface of a large-diameter substrate on a wafer level, thereby making mass production impossible. In particular, a thin, large-diameter wafer is susceptible to breaking during encapsulating the wafer.
For the purpose of avoiding these problems against a device-mounting substrate or a device-forming wafer, having a large diameter, it is known to lower the contraction stress upon curing by using a resin composition for encapsulation with a filler added thereto by about 90% by mass, or a resin composition for encapsulation with lower elasticity (Patent Documents 1, 2, and 3).
Unfortunately, such methods, for lowering the contraction stress, brings new problems as follows: Adding a filler by about 90% by mass to a resin composition for encapsulation increases the viscosity of the composition, resulting in an increasing force exerting on semiconductor devices, mounted on the substrate when the composition is casted and molded for the encapsulation, so that some of the semiconductor devices are peeled away from the substrate; Using the resin composition for encapsulation with lower elasticity leads to low encapsulation performance, such as heat resistance and humidity resistance, although it suppresses warping of the encapsulated device-mounting substrate or device-forming wafer. These conventional methods thus cannot solve the problems fundamentally. There is therefore a need for an encapsulant that has excellent encapsulation performance, such as heat resistance and humidity resistance after encapsulation, and enables the device-mounting surface of a substrate or the device-forming surface of a wafer to be collectively encapsulated on a wafer level without warp of the substrate or wafer and peeling of a semiconductor device away from the substrate, even when a large-diameter wafer or a large-diameter substrate such as a metal substrate is encapsulated.